Typically today, digital networks that provide for dynamic routing of network connections do not offer a practical method for establishing a preferred connection in a multi-peer group network. Currently, switches, such as the BPX 8600 switch available from Cisco Systems Incorporated of San Jose, Calif., provide the capability of establishing preferred routes but do not provide the dynamic routing of connection-based protocols. To illustrate this situation, a brief explanation of digital networks and dynamic routing is provided below.
A digital network is comprised of a group of switches (nodes) that are connected to each other through a variety of interfaces. Asynchronous Transfer Mode (“ATM”) or “cell switching” is a technology designed for transmitting digital information such as voice, video, and data at high speeds through the digital network. The digital information is segmented into cells (fixed-length packets) and transmitted from a source node through various intermediate nodes to a destination node. The path traversed through the network is known as a connection.
A digital network may employ virtual circuits that appear to be a discrete physical circuit dedicated to a particular user, but are actually a shared pool of circuit resources used to support multiple users. A permanent virtual circuit (PVC) is a continuously dedicated virtual circuit while a switched virtual circuit (SVC) is a temporary virtual circuit that may be dynamically established on demand, but is maintained only for the duration of a data transfer session. A hybrid of the PVC and the SVC is the soft permanent virtual circuit (SPVC) that has a PVC at the end points with a SVC within the network. This provides the user with the appearance and benefit of a PVC, but allows the network to intelligently reroute calls to accommodate node failures and optimize bandwidth utilization.
FIG. 1 illustrates an exemplary digital network employing a connection-based signaling protocol in accordance with the prior art. This allows the establishment of a static connection between two endpoints. Network 100 includes a plurality of nodes that are interconnected by network connections, which transfer data from an originating customer-premise equipment (CPE) node, CPE1, to a terminating CPE node CPE2. Each CPE node is terminating hardware such as a workstation, a computer, a server, or similar device that is owned by the user and not a service provider.
In general, the network 100 may include a variety of networks (e.g., ATM) coupling a plurality of users. For example, Network 100 employs a SPVC so that an SVC connects CPE1 to node A1 (source node), and CPE2 to node C6 (destination node), while the intermediate connections, through nodes A1, A3, A5, A6, B1, B2, B6, B7, C1, C4, and C6, are SVCs. In general, a connection between users (or between particular nodes) may be established by traversing various combinations of the intermediate nodes.
Typically, to establish a connection in a source-based routing protocol, such as Private Network-to-Network Interface (“PNNI”), a source node will compute an end-to-end route through the network and provide it in a designated transit list (DTL). The DTL is contained within a setup message that is transmitted from the source node A1 through the network to the destination node C6. The DTL contains a list of the nodes and ports that the connection will traverse from the source node A1 to the destination node C6. The DTL stores the routing information in the context of a hierarchical model as described below.
Networks may contain hundreds or thousands of nodes and it is not efficient for each node to be aware of every other node in the network. Typically the network nodes are arranged into peer groups (sets of local nodes), shown in FIG. 1 as peer groups A, B, and C. In order to reduce the amount of information used to compute end-to-end routes, each node is only aware of the details of nodes within its peer group. Remote peer groups are viewed as hierarchical abstractions containing only border entry nodes. For example, in PNNI routing, the lower level node has only the visibility of all the lower level nodes in a peer group and views other peer groups as logical group nodes. FIG. 2 illustrates the concept of hierarchical abstractions applied to Network 100 in accordance with the prior art. Source node A1 is aware of all the nodes and links (connections between nodes) within peer group A and their traffic capability. However, as shown in FIG. 2, node A1 views peer groups B and C as logical entities only. That is, source node A1 is not aware of the intricacies of remote peer groups B and C, and does not have the capability to determine a route through them. Therefore, when source node A1 routes a connection through peer group B, it is the routing protocol at border entry node B1 that determines the connection path through peer group B to node B7. Each remote peer group has the logic to determine if they are a transit peer group (e.g., B) or a destination peer group (e.g., C).
Routing protocols rely on this nodal hierarchy for scalability and abstraction of topology information. In a hierarchical multi-peer group network using PNNI routing, the DTLs contain the lower level node identifiers and port identifiers for nodes within the local peer group (i.e., local to the source node). However, the DTLs contain only the logical group node identifiers and port identifiers for remote peer groups.
For certain important connections, a service provider may not want the route established through the automatic decision-making process of the routing protocol, but may wish to establish a preferred route. That is, the service provider may wish to specify the route based on criteria or information that is not available to the routing protocol. For example, preferred routes may be used to direct critical connections over reliable trunks. Upon specifying the preferred route for an SPVC, the exact route, as specified, will be used to route the connection. The routes are specified as a sequence of node identifiers and port identifiers. The PNNI routing will use the exact route and determine if a link has potentially enough resources to support a connection (e.g., perform Generic Connection Admission Control (GCAC)). If sufficient resources are available, the PNNI routing allows establishment of the connection.
Due to the hierarchical nature of the routing information stored in the DTLs, in a PNNI hierarchical network, support for preferred routes is not possible. Because, even though the detailed lower level node information can be specified as the route for each SPVC, the DTL cannot carry the detailed lower level node information of other peer groups. The source node cannot specify the detailed lower level information of other peer groups and the information can only be pushed into the DTL by the entry border nodes of each remote peer group.
Moreover, ATM Inter-network Interface (AINI) networks do not support preferred routes. The AINI protocol allows the interconnection of two or more ATMs networks without sharing the individual network topology (routing information). Because the DTL information is not transported across AINI links, there is no way for a source node to configure a preferred connection across an AINI network.